1. Field of the Invention
The present invention relates to a power assisting transmission system of a power assisting bike and, more particularly, to the power assisting transmission system of a power assisting bike capable of achieving forward and backward transmissions or a back pedaling brake effect by forward and backward pedaling.
2. Description of the Related Art
As disclosed in U.S. Pat. No. 6,595,072 entitled “Sensor of the pedaling force of a power assisting bike”, a transmission system of the power assisting bike comprises one or more pairs of screw gears. The screw gear is driven by a pedaling force to rotate in situ, and the other screw gear is engaged by the opposite screw gear installed on a shaft and driven to move horizontally in an axial direction. The screw gear has a resilience member installed at an end of the screw gear, and the resilience member and the shaft of the screw gear have an annular magnet moved synchronously with the screw gear. A fixed end disposed opposite to a displacing end of the magnet includes a Hall sensor installed thereon. Thus, the screw gear of the transmission system can produce a lateral force to detect an axial displacement of the screw gear to output a voltage signal to control a motor. The motor can output motive power to the power assisting bike to achieve the power assisting effect. However, when a crank of the power assisting bike is pedaled in a backward clockwise manually and a transmission shaft rotates clockwise (viewing from the direction from an end A1 to the other end A2 of a first transmission shaft A), a one-way ratchet B is installed between the first transmission shaft A and the first left-handed screw gear C capable of rotating the pair of gears counterclockwise. Thus, the first transmission shaft A rotates clockwise due to the one-way ratchet B, and the first screw gear C cannot be driven to rotate. Therefore, when a conventional power assisting bike is pedaling in a backward direction manually in an idle pedaling status, a chain gear G1 cannot be driven to rotate. Thus, the power assisting bike does not have any backward pedaling function, and it obviously requires improvements.